Herbivore experience with plant defense compounds influences acquisition of new flavor aversions

Abstract

Multiple experiments were conducted with a mammalian herbivore to determine how experience with plant secondary metabolites (terpenes and tannins) influenced acquisition of new aversions to diets containing these same plant metabolites. Goats ( Capra aegagrus hircus) were employed as behavioral models for this study. Twenty-four subjects were assigned to three treatment groups that received 20 days of experience with test diets: (A) terpene diet only; (B) tannin diet only; and (C) terpene and tannin diets offered singly on alternate days. In experiment 1, all subjects were offered both diets in a two-choice test to determine if experience affected diet preference. Both treatments A and B demonstrated significant preferences for the terpene diet, while treatment C subjects did not exhibit a diet preference. Both diets were offered to all subjects and immediately followed with a 150 mg/kg dose of lithium chloride (LiCl) in experiment 2. A two-choice preference test was conducted to determine if lithium-induced toxicosis would be associated with the least familiar diet. As in experiment 1, treatments A and B preferred terpene diet while treatment C did not demonstrate a preference. Lithium chloride exposure was specifically paired with one of the test diets in experiment 3. A two-choice preference test demonstrated that treatments A, B, and C acquired aversions to tannin diet when it was paired with LiCl administration. However, terpene-paired LiCl administration did not produce an aversion to the terpene diet in treatments A and B. Treatment C preferred tannin diet when the terpene diet was paired with LiCl. A novel flavor was added to the choice of diets in experiment 4. All subjects were offered citric acid (CA), terpene, and tannin-containing diets and immediately dosed with LiCl. Subjects that acquired aversions to the tannin diet in experiment 3 continued to avoid tannin diet in experiment 4 and preferred terpene diet while eating significant quantities of the novel CA diet. Only treatment C subjects with previous terpene-paired LiCl exposures demonstrated aversions to the CA diet. These results have implications for the conduct of flavor aversion studies and the application of flavor aversion learning (FAL).